DESIGN PATTERN CATALOG

 

Christopher Alexander says: “Each pattern describes a problem which occurs over and over again in our environment, and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever doing it the same way twice”

 

A design pattern names, abstracts, and identifies the key aspects of a common structure that make it useful for creating a reusable object-oriented design. The design pattern identifies the participating classes and instances, their roles and collaborations and the distribution of responsibilities. Each design pattern focuses on a particular object oriented design problem or issue. It describes when it applies, whether it can be applied in view of other design constraints, and the consequences and trade-offs of its use.

 

The  Design Catalog contains 23 design patterns. These design patterns are classified based on the criterion, called purpose. Patterns can have either creational, structural or behavioral purpose.

 

                                                                       

Scope		Purpose
		Creational	Structural	Behavioral
	Class	Factory Method	Adapter	Interpreter
	Object	·      Abstract Factory ·      Builder ·      Prototype ·      Singleton	·        Adapter ·        Bridge ·        Composite ·        Decorator ·        Façade ·        Flyweight ·        Proxy	·        Chain of Responsibility ·        Command ·        Iterator ·        Mediator ·        Observer ·        State ·        Strategy ·        Visitor

 

 

Creational patterns concern the process of object creation. Structural patterns deal with the composition of classes or objects. Behavioral patterns characterize the way in which classes or objects interact and distribute responsibility

 

 

Some of the design patterns implemented in the project are:

• Builder Pattern: Separate the construction of a complex object from its representation so that the same construction process can create different representations.
• Mediator Pattern: Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently.
• Façade Pattern: Provide a unified interface to a set of interfaces in a subsystem. Façade defines a higher level interface that makes the subsystem easier to use.
• Factory Pattern: Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.
• Singleton Pattern: Ensure a class only has one instance, and provide a global point of access to it.

 

Usage of these patterns in the project are explained in detail in the following pages.